Physical and geometric effects on the classical geodetic observations in small scale control networks

Establishing precise geodetic control networks is one of the most important issues in geodesy and land surveying engineering. The geodetic networks are still very important to monitor dams, landslides (especially in the rough topography areas) and tunnels where it is not practical or possible to collect GNSS observations. In the classical two-dimensional geodetic networks, reducing slope distances to the horizontal ones is an important task for engineers. These horizontal distances along with the horizontal directions are being used in the 2D geodetic adjustment. The common practice for this reduction is the utilization of vertical angles to reduce the distances using trigonometric rules. However, one faces systematic effects when using vertical angles. These effects are mainly due to refraction, the deflection of the vertical (DOV), and the geometric effect of the reference surface (sphere or ellipsoid). One of our motivations is firstly to quantify the above-mentioned effects. Secondly, we highlight the methods one can use so that the vertical angle does not influence the reduction of the distances due to the geometric, physical and refraction effects.